House Democrats on Thursday moved to advance an ambitious $2tn domestic policy package that would overhaul large swaths of the American economy, with House speaker Nancy Pelosi confident they would ultimately deliver the second pillar of Joe Biden’s legislative agenda.

“This is historic; it is transformative,” Pelosi said during a press conference on Thursday, as lawmakers debated the measure on the House floor.

After months of gridlock and intra-party warring, Pelosi expressed optimism that the House was on the cusp of passing the measure, just two weeks after the House gave final approval to a separate effort investing in the nation’s aging infrastructure.

With their paper-thin majority, Democrats can spare only a handful of defections on the package, called Build Back Better. Party leaders had hoped to pass the measure in tandem with the infrastructure bill, but a last minute objection from a small band of centrist Democrats concerned over the cost of the package derailed those hopes.

Pelosi said the House would proceed to a vote on the measure following the release of a cost estimate from the nonpartisan Congressional Budget Office, as requested by the group of centrists. The agency said it would complete the analysis on Thursday.

The package, which would spend nearly $2tn over 10 years, is expansive: it aims to dramatically reduce child care costs, provide universal pre-kindergarten for children, lower the cost of prescription drugs for seniors, expand Medicare to cover hearing aids and provide the largest ever investment in efforts to combat the climate crisis.

Biden argues that the plan is fully paid for by a slew of new proposals targeting millionaires and big corporations that currently pay nothing in federal tax.

Even if the House approves the legislation on Thursday, it faces a complicated path forward in the Senate, where any single Democrat could upend the fragile state of negotiations.

Two of the Senate’s 50 Democrats, Kyrsten Sinema of Arizona and Joe Manchin of West Virginia, have not yet committed to supporting the package, even as negotiators reshaped the climate and tax portions of the package to meet their demands.

Opening the debate on Thursday, Democrats touted the historic nature of the legislation. Congressman John Yarmuth of Kentucky, the chair of the House budget panel, which played a critical role in shaping the package, said any single element of the bill alone would be significant, but together they represent the “most consequential legislation for American families since the New Deal”.

“It’s a hell of a bill,” he said.

Democrats and Republicans sparred on the House floor over the economics of the plan. Republicans assailed it as reckless spending that would exacerbate the trend of rising inflation and slow economic growth. Democrats argued the opposite, that the bill would actually combat inflation while relieving many of the financial stressors Americans face, such as the cost of child care and prescription drugs.

Though many of the bill’s provisions remain broadly popular, including among Republicans, boiling economic discontent have sent Biden’s approval ratings tumbling.

Despite a mass vaccination campaign, falling unemployment and legislative achievements that include the passage of a nearly $2tn relief package in March and the bipartisan public works bill this month, 63% of Americans say he has not accomplished much after 10 months in office, according to a Washington Post-ABC News poll.

Facing daunting challenges in next year’s midterm elections, Democrats are hopeful that enacting Biden’s agenda in full will bring something of a reversal of fortunes for the party.